title: A hypervalent pentacoordinate boron compound with an N-B-N three-center four-electron bond.
abstract: For the purpose of synthesizing and characterizing hypervalent boron compounds with strong hypervalent interaction, we have prepared a boron compound with a tridentate ligand bearing two pyrimidine rings as nitrogen donors. X-ray analysis and molecular orbital calculations suggested that the boron compound was of hypervalent pentacoordinate structure with an N-B-N hypervalent bond. Thus, we have prepared the first hypervalent second row element compound with apical N coordination. A breakdown of energy contributions by DFT calculations revealed that the N-B-N bond energy of the pentacoordinate state ground state (13) was 2.8 kcal mol(-1). Implications were that the conjugation energy difference of 6.6 kcal mol(-1) (14.2-7.6 kcal mol(-1)) with the tetracoordinate state was a crucial factor for shifting stability toward the pentacoordinate structure.
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Hirano
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kojima
authors.forename: Yohsuke
authors.initials: Y
authors.lastname: Yamamoto